1. Technical Field
The present invention relates to a white ink composition and a recorded material using the same.
2. Related Art
White ink compositions containing a white pigment such as a metal oxide (titanium dioxide, zinc oxide, silica, alumina, magnesium oxide, etc.), barium sulfate, or calcium carbonate have been used in various printing methods. For example, for printing a color image on a recording medium whose base color is not white, such as a plastic or metal medium, a white ink composition may be used to cover the base color to enhance the color developability of the color image. Also, for recording a color image on a transparent sheet, a white ink composition may be used to form a white mask layer on the sheet for reducing the transparency of the color image.
Such a white ink composition may contain a fixing resin to fix the white pigment to the recording medium. JP-A-2009-96914 discloses a white ink composition for textile printing, containing a white pigment, a polyurethane resin having a glass transition temperature of −35 to 10° C. as a fixing resin, and a polyol having an SP value of 10 to 15.5 (cal/cm3)1/2 as a water-soluble organic solvent. This white ink composition is resistant to washing and rubbing, can exhibit high covering ability when it is used for a deep color cloth, and is highly stable in recording apparatuses. JP-A-2009-138077 discloses a white ink composition containing hollow resin particles as a white color material, and a polyurethane resin having a glass transition temperature of 50° C. or less as a fixing resin. This ink composition can produce white images having high rub fastness. JP-A-2009-138078 discloses a white ink composition containing hollow resin particles as a white color material and resin particles of another type having a larger average particle size than the hollow resin particles. This ink composition can produce white images having high rub fastness. JP-A-2006-96933 discloses an ink jet ink comprising a pigment, and two polymer compounds as a fixing resin for fixing the pigment: an amphiphilic polymer compound; and a polymer compound having a glass transition temperature of −30 to 60° C. According to this patent document, characters and images formed on various recording media with the ink jet ink are resistant to water, abrasion and bleeding, and the ink has a high ejection stability. The performance of the white ink composition and the quality of images formed with the ink composition depend significantly on the type and amount of the fixing resin.
If a urethane resin is used as a fixing resin, the recorded image exhibits high covering ability and high adhesion to the recording medium. However, the surface of the image is sticky, and the image is likely to adhere to other images when recording media are stacked on top of one another. Also, the use of a urethane resin as a fixing resin can enhance the covering ability of the image, but the rub fastness and water fastness are insufficient.